National Instruments Module SCXI-1503 Instrukcja Użytkownika Pobierz pdf (Strona 33)

Chapter 4 Theory of Operation

The major components of the SCXI-1503 modules are as follows:

• Rear signal connector

• SCXIbus connector

• SCXIbus interface

• Digital control circuitry

• Analog circuitry

The SCXI-1503 modules consist of 16 multiplexed input channels, each

with a software-programmable gain of 1 or 100. Each input channel has its

own lowpass filter. Each channel has a fixed 100 μA current excitation. The

SCXI-1503 modules also have a digital section for automatic control of

channel scanning, temperature sensor selection, gain selection, and

auto-zero mode.

Rear Signal Connector, SCXIbus Connector, and

SCXIbus Interface

The SCXIbus controls the SCXI-1503 module. The SCXIbus interface

connects the rear signal connector to the SCXIbus, allowing a DAQ device

to control the SCXI-1503 module and the rest of the chassis.

Digital Control Circuitry

The digital control circuitry consists of the Address Handler and registers

that are necessary for identifying the module, reading/setting calibration

information, setting the gain, and selecting the appropriate channel.

Analog Circuitry

The analog circuitry per channel consists of a fixed lowpass filter and an

amplifier with a software selectable gain of 1 or 100. The CJ SENSOR

channel has a lowpass filter buffered by a unity gain amplifier. The

channels and CJ SENSOR are multiplexed to a single output buffer.

Analog Input Channels

Each of the 16 differential analog input channels feeds to a separate

instrumentation amplifier with a programmable gain of 1 or 100. Each

channel has a fixed 100 μA current excitation. Then the signal passes

through a fixed 2-pole, 5 Hz lowpass filter.

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National Instruments Module SCXI-1503 Instrukcja Użytkownika Strona 33